JPH085910B2 - 16α-methylation method - Google Patents

Description

BACKGROUND OF THE INVENTION Corticoids having a 16α-methyl group are known to be useful anti-inflammatory agents. These are dexamethasone (9α-fluoro-11β, 17α, 21-trihydroxy-16α-methylpregna-1,4-diene-3,20-dione), flumethasone 6α, 9α-difluoro-11β, 17α,
21-trihydroxy-16α-methylpregna-1,4-diene-3,20-dione) and paramazone (6α-fluoro-11β, 17α, 21-trihydroxy-16α-methylpregna-1,4-diene-3,20 -Dione).

16-unsaturated corticoid (I) starting materials are known. U.S. Pat.Nos. 2864834, 3210341, 3839369
See Nos. 4031080 and 4277409.

Using the Grignard reagent, 16-unsaturated pregnane was
It is known to transform into α-methylpregnane.
The conjugated addition of 16α-methyl groups to 16-unsaturated-20-ketosteroids by means of the methyl Grignard reagent in the presence of copper salt catalysts is well known. Organic Reactions in Steroid Chemistry (Organic
Reactions in Steroid Chemistry), Vol.II, Jay
See Fried and J.A. Edwards, Van Nostrand Reinhold Co., New York, 1972, p. 75. The product of such a reaction is 16α-
Methyl-Δ ¹⁷ ( ²⁰ ) ^-20 -enolate, which according to Fried can be trapped as a 20-acetic acid ester,
See page 76. The addition can be 1,2 or 1,4 in a ratio of about 1: 1, but the addition of cuprous chloride gives the 1,4-addition exclusively in yields much greater than 90%.

US Patent No. 3231568 (JULIAN) is 1
The modification of 6-unsaturated progesterone to the corresponding 17α-hydroxy-16α-methylprogesterone is disclosed. However, Julian's Pregnane is a steroid A
- Because the ring is 3,5-cyclohexylene, had no delta ^4-3-ketone or delta ^{l, 4-3-different} alpha / beta-unsaturated ketone ketone type. In addition, the method of the invention uses 21-acylates that are sensitive to the Grignard reaction and can be hydrolyzed, while Julian disclosed a progesterone that is not C ₂₁ reactive. The Julian C ring contains no substituents and was therefore not sensitive to the oxidation reaction conditions. A further difference is that Julian entraps with acetate and that Julian's enol acetate is not reactive to the mild peracid conditions of the present process and therefore does not form the desired 17,20-epoxide (III). Is.

U.S. Pat. No. 4031080 (PALLADINO) uses copper for the conjugate addition reaction, but as Julian teaches, the relaxation and selective permutation of the present invention to produce the desired 17,20-epoxide (III). This produces an enol acetic ester that is non-reactive with acid reaction conditions. Parasino is 17α
17-but not hydroxy-16α-methylcorticoid
This produces α-bromo-16α-methylcorticoid.

Although the method of the present invention introduces the desired 17α-hydroxyl group, it is described in US Pat. No. 4,277,409 (WARNANT).
Transforms 16-unsaturated-21-acetic acid ester to 16α-methyl-21-acetic acid ester without inserting the essential 17α-hydroxyl group.

British Patent No. 2001990, the 16-unsaturated corticoid methylated with copper catalysts methyl Grignard, 16Arufa- give methyl -Δ ^{17 (20)} -20- magnesium bromide) enolate,
The 16-unsaturated corticoid (I) is converted to the corresponding 17α-hydro-peroxide by oxidation, which is then reduced to the corresponding 16α-methyl-17α, 21-dihydroxy-20-one 21-acetic acid ester. The method for converting to 16α-methylcorticoid (V) is disclosed. The process of the present invention does not produce 17α-hydroperoxide, but rather 17α, 20-epoxide (III)
Utilizing intermediates.

US Patent No. 3072686 (Wetstein) (WETTSTE
IN) discloses the transformation of 16-unsaturated progesterone into 17α-hydroxy-16α-methylprogesterone by reacting it with Grignard reagent and cuprous chloride. Wetstein is not reactive to the relaxed and selective peracid conditions of the present process and therefore produces Δ ¹⁷ ( ²⁰ ) ^-20 -enol acetic ester which does not form the desired 17,20-epoxide (III). To do.

Journal of American Chemical Society, 80, 4428 (J.Am.Chem.Soc.), 80, 3160 (1958)
And Journal of American Chemical Society, 80, 4428 (1958) both used Grignard reagents to transform 16-unsaturated progesterone into 16α-methylprogesterone, followed by peroxidation to 17α-.
It has been reported that a hydroxy group is introduced to produce 17α-hydroxy-16α-methylprogesterone. 17α-
Brominated hydroxy-16α-methylprogesterone,
Acylated to 21-acetoxy-17α-hydroxy-16α
Form a methyl steroid.

EJ Corey, Tetrahedron Letters, 26, 6019 (1
985), [Colly] discloses the reaction of a methylating agent (lithium dimethyl-caperate) with an α, β-enone in the presence of a trapping agent (chlorotrimethylsilane). The significant difference between Collie and this patent application is that the present invention produces a caperate methylating agent in-situ, whereas Collie used a preformed alkyl caperate. Similarly, A. Alexis
akis), Tetrahedron Letters, 27, 1047 (198
6), [Alexakis], discloses the reaction of a lithium alkyl-caperate with an unsaturated ester in the presence of trimethylsilyl chloride, showing an increased yield of alkylation product. However, while the present invention produces a caperate methylating agent in-situ, Alexisaki, like Collie, also uses preformed caperates.

U.S. Pat. No. 3,700,660 discloses a process for converting 20-acyloxy-17,20-epoxy steroids to 17α-acyloxy-20-keto steroids by using a strong acid. Where the process of the present invention uses 20-silyl, U.S. Pat. No. 3,700,660 (HEMPEL) uses 20-acetic acid ester. This significance is due to the Δ ¹⁷ ( ²⁰ ) -20 of the present invention.
-Enolsilane (II) is considerably more reactive than the corresponding 20-acylates of hemper, which limits the 20-acylates of hemper to non-functional steroids, whereas Δ ¹⁷ ( ²⁰ ) -20- Enolsilane (II) is Δ ⁴ -3-
It is to allow the epoxidation of the Δ ¹⁷ ( ²⁰ ) double bond in steroids with other double bonds such as keto, Δ ^1,4-3 -keto, Δ ⁹ ( ¹¹ )-and the like.

U.S. Pat.Nos. 3513163 and 4036831 are C
₂₁ and C ₁₁ trimethyl-siloxy ethers are disclosed. The substituent is an acyl group or a Grignard substituent (-
A ^{Mg-X) Δ 17 (20} ) -20-O- substituted steroids are known. See U.S. Patent Nos. 3072686, 3231568 and 4031080. Although disclosed, this Mg-X substituted compound cannot be isolated.

In US Pat. No. 3876633, 17α, 20-epoxy-16α-methyl-20-, in which the 20-O-substituent is an acyl group
O-substituted steroids have been disclosed. Claim 9th
See section.

Selective epoxidation of the Δ ⁹ ( ¹¹ ) double bond over the Δ ¹⁶ double bond in Δ ⁹ ( ¹¹ ), ¹⁶ -dienes is shown in US Pat. No. 3,876,633. U.S. Pat.No. 3876633,
Disclosed are 9β, 11β-epoxy-Δ ¹⁶ -steroids in which the A ring is reduced. 9β, 11β-Epoxy-6α
-Fluoro-21-hydroxypregna-1,4,16-triene-3,20-dione 21-acetic acid ester is described in U.S. Pat.
No. 1, Example 9 (b).

US Pat. No. 4036831 discloses a method of protecting the 11β-hydroxyl group of steroids with trimethylsilyl during a continuous reaction and continuous removal of the trimethylsilyl group by hydrolysis with 40-60% aqueous hydrogen fluoride.

SUMMARY OF THE INVENTION Δ ^{17 (20)} - steroid (IIA-C), 17α, 20- epoxide (IIIA-C) and 17α- silyl ether (IVA-C) is disclosed. In addition, 16-unsaturated corticoids (IA
-C), (1) contacting the 16-unsaturated corticoid (IA-C) with a methylating agent in the presence of a copper catalyst, and (2) contacting the product of step (1) with a silylating agent. Disclosed is a method for producing Δ ¹⁷ ( ²⁰ ) -steroid (IIA-C), which is characterized by

Also, starting with Δ ¹⁷ ( ²⁰ ) -steroid (IIA-C),
A method for producing 17α, 20-epoxide (IIIA-C), which comprises contacting it with a peracid, is also disclosed.

Alternatively, starting from a 16-unsaturated corticoid (IA-C), the 16-unsaturated corticoid (IA-C) is contacted with a methylating agent in the presence of a copper catalyst and a silylating agent. A method for producing Δ ¹⁷ ( ²⁰ ) -steroid (IIA-C) is also disclosed.

DETAILED DESCRIPTION OF THE INVENTION 16-Unsaturated corticoid (IA-C) starting materials are well known to those skilled in the art or can be readily prepared from known steroids by methods well known to those skilled in the art. For example,
U.S. Pat.Nos. 2773080, 2864834, 3210341, 3
No. 441559, No. 3461144, No. 3493563, No. 3839369,
See 4031080 and 4277409.

In the method of the present invention, Δ ⁴ -3-keto (A), Δ
^1,4 3-keto (B) and 3β-hydroxy-Δ ⁵ −
(C) It is not necessary to protect the C ₃ reactive group of the steroid. Three
The β-hydroxy-Δ ^5- (C) steroid may have its C ₃ -hydroxyl group (Ca) protected as a silyl ether (Cb), ether (Cc) or ester (Cd). See Chart C. Free hydroxyl groups (Ca) can be protected as ethers (Cc) or esters (Cd) as is well known to those skilled in the art. Protective Groups in Organic Synthesis
ups in Organic Synthesis), Theodora W.
Theodora W.Greene, Willie & Sons (W
iley & Sons), New York, 1981. Ether (Cc) is produced by methods well known to those skilled in the art. Steroid Reactions
s), edited by Carl Djerassi, Holden-Day, San Francisco, 196
See pages 7, 76-82. Free 3β-hydroxyl group (Ca)
Is not protected as an ether (Cc) or ester (Cd) during the silylation reaction, the free hydroxyl group is silylated to form a silyl ether (Cb). During the silylation reaction, an additional 1 equivalent of Grignard and silylating agent is consumed when the 3β-hydroxyl groups are liberated and silylated. Since the C ₃ protecting group is easily removed and changes the C ₃ protected form (Cb, Cc and Cd) to (A and C), the C ₃ protected form of the 3β-hydroxysteroid (C) is either unprotected or Equivalent to the free form (C). The protecting group remains until the hydrolysis of the 17α, 20-epoxide (acid or base). When subjected to acid hydrolysis and unstable C ₃ protecting group is acid (Cb and Cc), C ₃ protecting groups are removed. Similarly, performs basic hydrolysis, and when C ₃ protecting group is sensitive bases (Cd), C ₃ protecting groups are removed. If the C ₃ protecting group is not sensitive to the hydrolyzing agent, treat the C ₃ protected steroid with a suitable agent,
It must be removed C ₃ protecting group.

16 unsaturated corticoid (IA-C) is, delta ^4-3-keto (A) or delta ^{l, 4-3-keto} (B) corticoid, more preferably delta ^{l, 4-3-keto} (B) corticoid Is preferred. 16-unsaturated corticoid is C-
It is preferred to have the ring Δ ⁹ ( ¹¹ ) or 9β, 11β-epoxy. More preferably, the C-ring is 9β, 11β-epoxy. R ₆ is preferably hydrogen or a fluorine atom, and more preferably R ₆ is a hydrogen atom.

The C-ring is preferably Δ ⁹ ( ¹¹ ) or 9β, 11β-epoxy, but prior to Grignard addition of the methyl group to the Δ ¹⁶ double bond, the C-ring can be converted to the desired 9α-fluoro-11β.
It can be converted into a hydroxy-reactive group. When performing this procedure, the 11β-hydroxy group must be protected as is well known to those skilled in the art. See, for example, U.S. Patent No. 4036831, wherein the protecting group is trimethylsilyl. The desired one
After forming the 6α-methylcorticoid, the (trimethylsilyl) protecting group is removed by methods well known to those skilled in the art. See, for example, U.S. Pat. No. 4036831.

It is known that the conjugated addition of methylating agents such as methyl Grignard to 16-unsaturated steroids gives the corresponding 16α-methylcorticoids. Organic Reactions in Steroid Chemistry, Vol.II, Jay Fried and Jay A.
See Edwards (J. Friod and JA Edwards), page 75, and US Pat. No. 30,72,686.

Then or trapping (Sila)
The 16-unsaturated corticoid (I) is reacted with the methylating agent in the presence of a ting) agent to give the enolsilane Δ ¹⁷ ( ²⁰ ) -steroid (II). Rather than reacting the 16-unsaturated corticoid (I) with the methylating agent, it is possible to react the 16-unsaturated corticoid (I) with the methylating agent in the presence of the trapping agent, rather than adding the trapping agent. preferable. Methylating agent, CH ₃ Cu, is selected from (CH _{3) 2} CuM or CH ₃ MGQ and a catalytic amount of copper (cupric) the group consisting of salts. A preferred methylating agent is methyl Grignard, preferably methyl magnesium chloride. Copper salt is chloride
Cuprous salts such as cuprous bromide, iodide or cyanide,
Alternatively, it may be a cupric salt such as cupric chloride, cupric acetate, cupric propionate or a complex thereof. As an example of the copper complex, dimethyl sulfide cuprous bromide, tris-
n-Butylphosphine cuprous chloride and acetylacetone cuprous. The nature of the copper complex is not limited. Hundreds (or thousands) of copper complexes are known and they are considered equivalent to the above complexes. Acetic acid or cupric propionate is preferred, and cupric propionate is more preferred. In addition, catalysts that are considered equivalent to the above catalysts are well known to those skilled in the art. For example, Alfa Catalog, 1983-1984, Morton Thiokol, Inc., Alpha Products, Massachusetts 01923, Danvers and Bar Street 152.
Number PO Box 299, 152 Ando
See Ver Street, Danvers, Mass 01923). Due to physical ease, it is preferred to pre-dissolve the cupric propionate. Suitable solvent for methylation reaction is THF,
It includes a solvent selected from the group consisting of t-butyl methyl ether or dimethoxyethane. The reaction is about -50
C. to 20.degree. C., preferably about -20.degree.
If TLC shows no starting material left (indicative of possible formation of the enolate intermediate), the silylating agent is added and the product obtained is a Δ ¹⁷ ( ²⁰ ) steroid (II). After adding the silylating agent, the reaction temperature is maintained in the range of about -25 ° C to about 25 ° C, preferably about 0 ° C. It is preferred to filter the Grignard reaction mixture to prevent residual copper from entering the peracid reaction.

In the present invention, the enolate intermediate is trapped with a trapping (silylating) agent to give the Δ ¹⁷ ( ²⁰ ) -20- (substituted silyl) product. The silylating agent that can be used is
Including _{(R 20) 3 -Si-E} , bis trimethylsilyl acetamide. Silylating agent has the formula _{(R 20) 3 -Si-E} , further preferably a trimethylsilyl chloride. Silylating agents that are considered equivalent to the silylating agents are also well known to those skilled in the art. For example, Silicone Compounds, Petrarch System, Inc., Pennsylvania.
19007, Bertram Eardy Bristol (Bartr
am Rd. Bristol, PA 19007). The silylating agent may be present during the formation of the enolate or added after the enolate is formed, but it is preferred that the silylating agent be present during the formation of the enolate. It is known to trap the enolate intermediate to give Δ ¹⁷ ( ²⁰ ) -20- (acetate). See U.S. Patent No. 4031080 and Organic Reactions in Steroid Chemistry, Vol. II, supra at page 76. These enol acylates are very non-reactive and cannot control the A, B, C-ring reactivity such as Δ ⁹ ( ¹¹ ) and selectively react. But surprisingly and surprisingly,
The Δ ¹⁷ ( ²⁰ ) -20- (substituted silyl) derivative (II) is sufficiently reactive to react with electrophilic reagents without affecting the other reactivities at the A, B, C-rings.

The Δ ¹⁷ ( ²⁰ ) -steroid (II) can be isolated, if desired, by means well known to those skilled in the art. For example, Example 1
See 8 and 8. However, since the desired product is 16α-methylcorticoid (V), it does not need to be isolated and Δ
It is preferred not to isolate the ¹⁷ ( ²⁰ ) -steroid (II) but rather continue the reaction. See Examples 3-5, 11 and 12.

Δ ¹⁷ ( ²⁰ ) -steroid (II) is reacted with peracid to give 17
The α, 20-epoxide (III) is obtained. Although most peracids can be used, preferred peracids include m-chloroperbenzoic acid, perbenzoic acid, peracetic acid. Peracid reaction conditions are well known to those skilled in the art. The peracid reaction does not significantly affect Δ ¹ , Δ ⁴ , or Δ ⁹ ( ¹¹ ) reactivity in the rest of the molecule. See Example 2. Δ ¹⁷ ( ²⁰ ) -steroid (I
The solvent used during the methylation reaction to produce I) is removed and replaced with a non-polar solvent such as toluene, methylene chloride, ethyl acetate or t-butyl methyl ether. The remaining inorganic salt after the methylation reaction is removed by extraction. The peracid oxidation is carried out in the temperature range of about -30 ° C to 25 ° C, preferably about -20 ° C. When the reaction is complete, a reagent such as powdered sodium thiosulfate or sodium bisulfite is added to quench excess peracid. 17α, 20−
The epoxide (III) can optionally be isolated by means well known to those skilled in the art. However, since the desired product is 16α-methylcorticoid (V), it is not necessary to isolate it, and it is preferable not to isolate 17α, 20-epoxide (III), but rather to continue the reaction in the system. .

The 17α, 20-epoxide (III) is converted to the corresponding 16α-methylcorticoid (V) by acid or base hydrolysis. When a base is used, 16α-methylcorticoid is obtained as a 21-hydroxy compound (R ₂₁ is a hydrogen atom). When using an acid, 16α-methylcorticoid is 21-
It is an ester (R ₂₁ is —CO—R ₂₁ ′). Suitable base hydrolysis agents include hydroxides, carbonates, bicarbonates, alkoxides, etc. in alcohol at low temperature. The hydrolyzing agent is preferably an acid. Suitable acids include mineral acids such as p-TSA, sulfuric acid, hydrochloric acid, citric acid or acetic acid and other sufficiently strong acids. Acid hydrolysis is fast enough and the reaction is 20
It takes about 1/2 hour at ~ 25 ℃.

As well known to those skilled in the art, 16α-methylcorticoid (V) is an adrenocorticoid agent having glucocorticoid activity and is mainly useful as an anti-inflammatory drug. These include dexamethasone, flumethasone and parametricsone. One of the best known 16α-methylcorticoids is dexamethasone. U.S. Pat. No. 3,375,261 and Reissue No. 28369 and Physicians Desk Refe
1983, 37, pp. 1270-1283.

The C-ring of 16α-methylcorticoid (V) is
When it is Δ ⁹ ( ¹¹ ) or 9β, 11β-epoxy, it can be easily converted into a pharmacologically active 9α-fluoro-11β-hydroxy C-ring by means known to those skilled in the art.

Definitions The following definitions and explanations are for terms used throughout the patent application, including both the specification and the claims.

 All temperatures are in degrees Celsius.

 TLC refers to thin layer chromatography.

 THF refers to tetrahydrofuran.

 TMS refers to trimethylsilyl.

 THP refers to tetrahydropyranyl.

EEE is (1-ethoxy) ethyl ether [-O-CH (C
H ₃ ) OCH ₂ CH ₃ ].

 p-TSA refers to p-toluenesulfonic acid monohydrate.

When solvent pairs are used, the ratio of solvents used is volume / volume (v / v).

 DMSO refers to dimethyl sulfoxide.

 UV refers to ultraviolet spectroscopy.

NMR refers to nuclear (proton) magnetic resonance spectroscopy, the chemical shift is PPM from a low magnetic field from tetramethylsilane.
Reported in (f).

[Α] _D ²⁵ refers to the angle of rotation (specific optical rotation) of the plane of polarization using the sodium D line (5893A) at 25 ° C.

Dexamethasone is 9α-fluoro-11β, 17α, 21-trihydroxy-16α-methylpregna-1,4-diene-
3,20-refers to dione.

Parameterzone is 6α-fluoro-11β, 17α, 21-trihydroxy-16α-methylpregna-1,4-diene-3,2
0-refers to dione.

Flumethasone is 6α, 9α-difluoro-11β, 17α, 21
-Trihydroxy-16α-methylpregna-1,4-diene-3,20-dione.

R ₃ is alkyl having 1 to ₃ carbon atoms, TMS, THP or EE
It is group E.

R ₃ 'is alkyl or phenyl having 1 to 5 carbon atoms.

R ₆ is hydrogen, a fluorine atom or a methyl group.

R ₉ Hanashika, hydrogen, fluorine or oxygen atom, it is, C-ring a) a case of R ₉ Ganashi, delta ^{9 (11),} and b) R ₉ and R ₁₁ together oxygen atom If so, the 9β, 11β-epoxide is used.

R ₁₁ is a hydrogen or oxygen atom, 2 hydrogen atoms, or an α- or β-hydroxyl group or its trimethylsilyl ether, which is a C-ring, a) Δ ⁹ ( ¹¹ ) when R ₁₁ is a hydrogen atom. B) R ₉ and R ₁₁ are taken together to form an oxygen atom, and between C ₁₁ and R ₁₁ Is a single bond, 9β, 11β-epoxide, and c) R ₁₁ is an oxygen atom, and between C ₁₁ and R ₁₁ . If is a double bond, it is a ketone.

R ₂₀ is alkyl having 1 to 4 carbon atoms or phenyl, and R ₂₀ may be the same or different.

R ₂₁ is hydrogen atom, -CO-R ₂₁ 'or Si (R _{121) 3.}

R ₂₁ ′ is alkyl having 1 to 4 carbon atoms or phenyl.

R ₁₂₁ is alkyl having 1 to 4 carbon atoms or phenyl, and R ₁₂₁ may be the same or different.

~ Indicates that the linking group can be either in the α or β sequence.

Is a single or double bond.

When the term "alkyl having _ to _ carbon atoms" is used,
If the isomer exists, such a thing is also meant and included.

X is a hydrogen atom or unsubstituted; X is a case of no, the C ₃ Is a double bond, and when X is a hydrogen atom, C ₃ Is a single bond.

 M is lithium or magnesium ion.

 Q is a chlorine, bromine or iodine atom.

E is chlorine, bromine or iodine atom or -NR α R _β.

R _α is alkyl having 1 to 5 carbon atoms or phenyl, and may be bonded or cyclized with R _β in the ring with or without an oxygen or further nitrogen atom.

R _β is alkyl or phenyl having 1 to 5 carbon atoms and may be bonded or cyclized with R _α in the ring with or without oxygen or even a nitrogen atom.

Examples Those skilled in the art can use the previous description and expect that the invention can be practiced to the maximum extent without further ado. The following detailed examples describe how to make various compounds and / or carry out various methods of the present invention, which are provided by way of illustration only and in no way limited to the preceding disclosure. It should be interpreted as not. One of ordinary skill in the art will immediately recognize suitable variations from both procedures for the reactants and for the reaction conditions and techniques.

Example 1 20,21-Dihydroxy-16α-methylpregna-1,4,9 (11), 17 (20) -tetraen-3-one 20-
Trimethylsilyl ether 21-acetic acid ester (IIB) was preliminarily -52 with methyl magnesium chloride in 4.5 ml of 2M THF.
21-Hydroxypregna-1,4,9 (11), 16 cooled to ℃
-Tetraene-3,20-dione 21-acetic acid ester 2.0 g (I
B, US Pat. No. 4031080), a mixture of 27 ml THF and 60 mg cupric acetate monohydrate over 2.5 hours.
The reaction temperature is kept below -40 ° C during the Grignard addition. After Grignard addition, TLC showed no starting material left and the reaction mixture was treated with trimethylsilyl chloride 1.1 m
Quench with l. The reaction temperature was then slowly raised to 4 ° C. over 3 hours, at which time TLC showed the reaction was complete. Add 15 ml of toluene and add the reaction medium.
THF is removed under reduced pressure while maintaining at 10 to 15 ° C. The reaction mixture is extracted first with pH 7 buffer, then 4 times with 1 ml buffer and 9 ml water and finally with water. The layers are separated and the organic layer is dried over sodium sulphate for 48 hours below 0 ° C.
The toluene solution is divided into 35 ml for 2 minutes and one of them is concentrated under reduced pressure to give the title compound.

Example 2 17α, 21-dihydroxy-16α-methylpregna-1,4,9 (11) -triene-3,20-dione 21-acetic acid ester (VB) 0.556 g of m-chlorobenzoic acid was added at about -9 ° C. About 0 ℃
While maintaining the bath temperature in the range of 20,21 for about 3 hours
-Dihydroxy-16α-methylpregna-1,4,9 (11),
17 (20) -tetraen-3-one 20-trimethylsilyl ether 21-acetic acid ester (IIB, Example 1, one 35 m
l part). The reaction mixture was 1M sodium bisulfite 2.8 ml
To quench. Water is added and the phases are separated. The organic phase is washed with water, buffer and water, dried over sodium sulphate and concentrated to a solid. 5 ml of solid ethyl acetate / hexane
Dissolve in and allow crystals to form overnight. The filtrate is concentrated to a solid, it is dissolved in methanol and cooled to 0 ° C. The mixture is filtered and the crystals washed with cold methanol.

TLC shows the presence of some 21-hydroxy compound (V). 0.1 ml acetic anhydride and 0.4 ml pyridine are added and the mixture is stirred overnight. The mixture is worked up as is well known to those skilled in the art to give a solid which is crystallized from 40% aqueous methanol to give the title compound.

Example 3 9β, 11β-epoxy-17α, 21-dihydroxy-16α-methylpregna-1,4-diene-3,20-dione 21-acetic acid ester (VB) 9β, 11β-epoxy-21-dihydroxypregna
1,4,16-triene-3,20-dione 21-acetic acid ester 3.82
4 g (IB, Example 7) and cupric acetate monohydrate 200 mg
And a mixture of 70 ml of anhydrous THF are treated with 8.2 ml of 2.2M methylmagnesium chloride added dropwise at -15 ° C over 1 hour. After stirring for 10 minutes at -15 ° C, trimethylchlorosilane
Add 1.64 ml. The mixture was immediately warmed to 20 ° C. and stirred for 1 hour, at which time TLC indicates complete enol ether (II) formation. The mixture is added to 100 ml of toluene, which is washed with 50 ml of monobasic phosphate buffer (pH 4.25). The organic layer was separated, washed with water (2 x 50 ml),
Each aqueous layer is back extracted with 15 ml of toluene. Combine the organic phases, 55
Concentrate to a residue under reduced pressure at ° C.

30 ml of toluene are added at 0 ° C. and the mixture is treated with 2.91 ml (34.5%) of peroxyacetic acid containing 164 mg of sodium acetate. The stirred mixture was warmed to 20 ° C. and after 10 minutes TLC showed the peroxidation was complete. Excess peracid, 10 ml of methanol
Quenched by adding 2.5 g of powdered sodium thiosulfate slurried in. Add 3.0 ml of 6N hydrochloric acid and add about 10
The hydrolysis is complete in minutes. The mixture is added to 75 ml of toluene and the organic phase is water (2 x 50 ml), 5% sodium carbonate solution.
Wash with 40 ml and finally with 50 ml water. Toluene for each aqueous phase
Back-extract continuously with 20 ml. The organic phases are combined and concentrated under reduced pressure to a crystalline residue, which is dissolved in hot ethyl acetate, filtered and freed from traces of minerals. Ethyl acetate (about 5 ml) is used for rinsing. The combined volume of filtrate and rinse is reduced to about 10 ml. A solid forms and after about 1 hour 4 ml of hexane are added. After leaving it at 30-40 ℃ for 2 hours,
Cool the slurry to 20 ° C. and collect the solids by vacuum filtration. The solid is washed with cold ethyl acetate: hexane, 1: 1 (3 ml) and dried under reduced pressure at 50-60 ° C for 3 hours to give the title compound with a melting point of 180-186 ° C which softens at about 135 ° C. NMR (CDCl ₃ )
0.89, 0.92, 1.43, 3.18 and 4.83δ. Example 4 9β, 11β-epoxy-6α-fluoro-17
α, 21-dihydroxy-16α-methylpregna-1,4-diene-3,20-dione (VB) 9β, 11β-epoxy-6α-fluoro-21-hydroxy-1,4,16-triene-in 120 ml of anhydrous THF 8.009 g of 3,20-dione 21-acetic acid ester (IB, U.S. Pat.
No.), 400 mg of cupric acetate monohydrate and 1 ml of tri-n-butylphosphine are treated with 26.5 ml of 1.95M methylmagnesium chloride added dropwise at -11 ° C over 1 hour. Then trimethylchlorosilane 4m at -8 ℃
add l The mixture was immediately warmed to 14 ° C. and after 20 minutes TLC showed the reaction was complete. 300 ml of ethyl acetate mixture
In addition, ammonium hydroxide: saturated ammonium chloride,
Wash 1: 1 (2 x 75 ml). Each aqueous extract is washed successively with 210 ml of the same portion of ethyl acetate. The combined organic phases are then concentrated at 45 ° C. under reduced pressure to an oil. The oil was dissolved in 120 ml of methylene chloride at −10 ° C. and treated with 6.092 g of 85% m-chloroperoxybenzoic acid, after 1.5 hours TLC shows that the epoxidation is complete. The mixture is vacuum distilled, the solvent is replaced with 100 ml of methanol and then the mixture is treated with 20 ml of saturated sodium carbonate. 16 hours and 55 at 20-25 ° C
After stirring for 5.25 h at ° C, TLC showed the hydrolysis was complete. After cooling to 20-25 ° C, 100 ml of water are added and the pH is adjusted to 7.5 with 0.2 ml of acetic acid. Then 5 ℃
Then add 160 ml of water little by little. The solid formed is collected by filtration, washed with 50 ml of methanol (75:25) in water at 0 ° C. and dried under reduced pressure at about 84 ° C. for 16 hours to give the title compound. Melting point 241-241.5 ° C; [α] _D ²⁵ = + 45.7 °
(DMSO); UVλmax = 245nm (ε = 15300); NMR (CDCl ₃ / DM
SO-d ₆₎ 0.82,0.82,1.40,3.30,4.30 and 5.52Deruta. Example 5 17α, 21-Dihydroxy-16α-methylpregna-4,9 (11) -diene-3,20-dione 21-acetic acid ester (VA) 6.2 ml of 2M methylmagnesium chloride in THF and dry THF1.
21-Hydroxypregna-4,9 (11), 16-triene-3,20-dione 21-acetic acid ester 3.68 g (IA, U.S. Pat. No. 4,216,159) and cupric acetate monohydrate 200 mg in 00 ml. To the above mixture at -50 ° C over 17 minutes. The mixture is stirred for 20 minutes at -45 to -50 ° C, then treated with 1.9 ml of trimethylchlorosilane and warmed to 20-25 ° C. 2
After 1.5 hours at 0-25 ° C, TLC shows the enol silyl ether formation is complete. The reaction mixture is ethyl acetate 15
In 0 ml, the mixture is washed with 200 ml of 5% cold sulfuric acid, the layers are separated and the aqueous layer is back extracted with 25 ml of ethyl acetate. The first organic layer was washed with cold water (2 x 150 ml) and then back extracted with additional ethyl acetate. Combine the organic layers and combine under reduced pressure for approx. 100 m.
Concentrate to l.

1.72 g of 85% m-chloroperoxybenzoic acid was added and the mixture was stirred at -15 ° C for 1 hour, after which 300 m of peracid was added.
g is added and the mixture is stirred at 20 ° C. overnight. Excess peracid is destroyed by treatment with 20 ml of 10% sodium bisulfite solution. The mixture is stirred for 20 minutes, then toluene 20
Dilute with 0 ml. The mixture is then washed with 100 ml of 5% sulfuric acid and water (2 x 100 ml). After concentration to dryness under reduced pressure, the residue is dissolved in 100 ml of methanol and treated with 0.5 ml of 3N hydrochloric acid. The mixture is concentrated again to a high-boiling residue, which is dissolved in 200 ml toluene. The mixture was added to saturated sodium carbonate 100
Wash with ml to remove m-chlorobenzoic acid. Finally the organic layer is washed with water (2 x 100 ml) and concentrated as above. The residue is dissolved in 20 ml of hot methanol for crystallization. 0
After cooling to ° C for several hours, a solid is obtained which is collected by vacuum filtration. The product is washed with cold methanol and dried at 20 ° C to give the title compound. NMR 0.73, 0.93, 1.33 and 4.9
8δ. Example 6 9β, 11β-Epoxy-21-dihydroxypregna-4,16-diene-3,20-dione 21-acetic acid ester (IA) 21-hydroxypregna-4,9 (11), 16-triene-
3,20-dione 21-acetic acid ester (U.S. Pat.
The title compound is obtained according to the general procedure of US Pat. Melting point 129-130.5 ° C.

Example 7 9β, 11β-epoxy-21-hydroxypregna-1,4,16-triene-3,20-dione 21-acetic acid ester (IB) 21-hydroxypregna-1,4,9 (11), 16-Tetraene-3,20-dione 21-acetic acid ester (U.S. Pat.
The title compound is obtained according to the general procedure of U.S. Pat. No. 3,876,633, without any critical deformation, except starting at 834). Melting point 163.5-165 ° C.

Example 8 9β, 11β-Epoxy-17α, 21-dihydroxy-16α-methylpregna-1,4-cyen-3,20-dione (VB) 9β, 11β-Epoxy-21-hydroxypregna-1 in 130 ml of dry THF. A mixture of 7.650 g of 4,4,16-triene-3,20-dione 21-acetic acid ester (IB, Example 7) and 400 mg of cupric acetate monohydrate is stirred under nitrogen. The temperature is adjusted to -20 ° C and 5.0 ml of 1,1,3,3-tetramethylurea is added. 2M methylmagnesium chloride 16.6 ml -17 to-
Add dropwise at 19 ° C over 50 minutes. TLC shows that the Grignard reaction is complete. The mixture is stirred for 40 minutes at -19 ° C, after which the magnesium enolate is quenched with 3.28 ml of trimethylchlorosilane. The temperature rises to 25 ° C during 1 hour of stirring. TLC shows the reaction is complete. The mixture is added to 150 ml of toluene and 50 ml of monobasic potassium phosphate buffer (pH 4.3, 10%). The aqueous layer is extracted with 25 ml of toluene and then discarded. The two organic layers are washed successively with water (2 x 50 ml), then combined and concentrated to a high boiling residue.

The residue containing Δ ¹⁷ ( ²⁰ ) ^-20 -enolsilane was added to toluene.
Dissolve in 60 ml. After cooling to -5 ° C, 5.9 ml 4.4M peroxyacetic acid containing 91 mg sodium acetate are added and the mixture is stirred for 80 minutes. TLC shows the epoxidation is complete. Excess peracid was added at about 0 ° C with 1.5M aqueous sodium bisulfite 10
Erase with ml. After 5 minutes of stirring, the mixture is added to 40 ml of toluene and 55 ml of water. The layers are separated and the aqueous phase is toluene 20 ml.
Extract with and then discard. The two organic layers are washed successively with 20 ml saturated sodium bicarbonate and 35 ml water. The combined organic layers are filtered through cotton cloth and concentrated to a high boiling residue of 17α, 20-epoxide.

The epoxide was dissolved in 60 ml of methanol and p- at 21 ° C.
Treat with 5 ml TSA. After 6 minutes, TLC shows that the epoxide has cleaved to form 16α-methylcorticoid (as the 21-acetic acid ester). Saturated sodium carbonate solution 1.
9 ml are added and the slurry is stirred at 55 ° C. for 45 minutes. TLC shows the hydrolysis is complete. 30 ml of water was added and the slurry was stored at 0 ° C overnight. The solid is collected by filtration, washed with methanol / water (1/1) and dried under reduced pressure at 70 ° C for 4.5 hours to give the title compound. Melting point 238-239.5 ° C.

Example 9 9β, 11β-Epoxy-20,21-dihydroxy-16α-methylpregna-1,4,17 (20) -triene-3
-On-20-trimethylsilyl ether 21-acetic acid ester (IIB) 9β, 11β-epoxy-21-dihydroxy-1,4,16-
The title compound is obtained according to the general procedure of Example 1 without any critical transformation, but starting with the triene-3,20-dione 21-acetic acid ester (IB, Example 7).

Example 10 9α-Fluoro-11β, 21-dihydroxypregna-1,4,16-triene-3,20-dione 21-acetic acid ester (IB) 9β, 11β-epoxy-21-hydroxypregna-1,
4,16-triene-3,20-dione 21-acetic acid ester 15.3 g
(IB, Example 7) at -25 ° C equipped with a mechanical stirrer 20
Add to a stirred mixture of 55 ml 72% aqueous hydrogen fluoride and 15 ml methylene chloride in a 0 ml monel reactor. Use about 30 ml of methylene chloride as a rinse. The mixture is stirred at -22 ° C for 2.5 hours and then at -4 ° C to -11 ° C for 4.0 hours. Mix the mixture at -10 ℃
Treat with 35 ml of HF, then carefully quench by slow addition of a mixture of 60 ml of THF, 202 ml of 47% aqueous potassium carbonate and 100 ml of water. After stirring for 20 minutes, the mixture is added to 400 ml toluene and 400 ml water. The phases are separated, the organic layer is washed with water (3 x 150 ml), dried by filtration through cotton cloth and concentrated to about 150 ml. Methylene chloride (about 150 ml) and 0.90 g of magnesol are added to the mixture. After 15 minutes, the magnesol is removed by filtration. The filtrate is concentrated again to 150 ml and then cooled to 0 ° C. After stirring for 3 hours at 0 ° C., a solid formed and the product was collected by filtration. The solid is washed with toluene (2 x 25
ml) and dried under vacuum at 60 ° C. for 3 hours to obtain the title compound. Mp _{223~225 ℃; NMR (CDCl 3)} 1.27,1.59,4.29,
4.93 and 6.77δ. Example 11 9α-Fluoro-11β, 20,21-trihydroxy-16α-methylpregna-1,4,17 (20) -triene-
3-one 11,20-bis (trimethylsilyl) ether 21
-Acetic ester (IIB) A solution of 151 mg of copper (II) propionate in 60 ml of dry THF is cooled to -30 ° C and then treated with 2M methylmagnesium chloride (about 1 ml) to reduce the copper to copper (I). To do. 9
α-Fluoro-11β, 21-dihydroxypregna-1,4,1
6-triene-3,20-dione 21-acetic acid ester 2.025 g (I
B, Example 10) is added to the copper mixture. The temperature is adjusted to -33 ° C and 3.0 ml of the Grignard reagent is added. A slurry forms which is treated with 1.50 ml of trimethylsilyl chloride to dissolve. After stirring at -40 ℃ for 1 hour, 7.4m
Add 1 Grignard reagent in small portions over 50 minutes. The mixture is stirred for a further 2 hours and the temperature is raised to -26 ° C. 2.0 ml of trimethylsilyl chloride are then added at -15 ° C over 1.25 hours. After an additional 0.5 h at −15 ° C., TLC shows that the formation of Δ ¹⁷ ( ²⁰ ) -enol ether is not complete. Add 3.0 ml of Grignard reagent to -35 ° C.
Add in. After 20 minutes the mixture is added to 150 ml toluene. The mixture is washed with 150 ml of water containing 20 ml of 5% phosphate buffer (pH 6.5). The phases are separated, the organic layer is washed with water (2 × 75 ml) and then dried by filtration through a cotton cloth to give the title compound in solution.

Example 12 17α, 20-epoxy-9α-fluoro-11β,
20,2-Trihydroxy-16α-methylpregna-1,4-
Dien-3-one 11,20-bis (trimethylsilyl) ether 21-acetic acid ester (IIIB) The filtrate (Example 11) was concentrated to about 50 ml, the mixture was cooled to -17 ° C and 67 mg of sodium acetate was added. Contains 4.
Add 3.37 ml of 44M peroxyacetic acid. The mixture is stirred for 4 hours while raising the temperature to 7 ° C. The mixture is diluted with toluene and then washed with 75 ml water, dilute sodium sulfite and finally 75 ml water. Each water washing solution is back-extracted with 50 ml of toluene. The organic phases are combined and concentrated under vacuum distillation to give a crude 17
A high boiling residue of (20) -epoxide-20-trimethylsilyl ether (III) is obtained.

Example 13 9α-Fluoro-11β, 17α, 21-trihydroxy-16α-methylpregna-1,4-diene-3,20-dione 21-acetic acid ester (VB) The residue (Example 12) was dissolved in 30 ml of methanol, Let stand at room temperature. After 0.75 hours, the mixture was concentrated to 15 ml and washed with water.
Add 10 ml. The mixture is filtered to remove traces of insoluble material. The filtrate is further diluted with water and the waxy solid is collected by decantation. The solid is dried and then recrystallized from acetone / hexane (1/2, 35 ml). The solid is collected by filtration, washed with acetone / hexane (1/2, 5 ml) and dried at room temperature to give the title compound. A pure sample of the title compound is obtained by column chromatography, followed by crystallization from acetone / hexane (1/1). Mp 227-229 ° C; NMR (CDCl ₃ ) 0.89, 1.03, 1.5
7, 4.29 and 4.93δ. Example 14 17α, 20-epoxy-20,21-dihydroxy-
16α-Methylpregna-1,4,9 (11) -triene-3-
On 20-trimethylsilyl ether 21-acetic acid ester (IIIB) 20,21-dihydroxy-16α-methylpregna-1,4,9
(11), 17 (20) -Tetratoen-3-one 20-trimethylsilyl ether 21-acetic acid ester (IIB, Example 1)
Following the general procedure of Example 12 the title compound is obtained.

Example 15 9β, 11β, 17α, 20-diepoxy-20,21-dihydroxy-16α-methylpregna-1,4-diene-3
-One 20-trimethylsilyl ether 21-acetic acid ester (IIIB) 9β, 11β-epoxy-20,21-dihydroxy-16α-
Methylpregna-1,4,17 (20) -trien-3-one 20
-Trimethylsilyl ether 21-acetic acid ester (IIB,
The title compound is obtained according to the general procedure of Example 12 without making any critical transformations, except starting from Example 9).

Example 16 9β, 11β-epoxy-17α, 21-dihydroxy-16α-methylpregna-1,4-diene-3,20-dione 21-acetic acid ester (VB) Copper propionate (II) in 90 ml THF and 5 ml tetramethylurea. ) 802 mg of the mixture are cooled to -25 ° C. under nitrogen and treated with about 3 ml of 2M methylmagnesium chloride in order to convert the bronze (II) into brass (I) species. Then methylene chloride
90 ml, trimethylsilyl chloride 6.56 ml and 9β, 11β-
15.30 g of epoxy-21-hydroxypregna-1,4,16-triene-3,20-dione 21-acetic acid ester (IB, Example 7) is added and the temperature is lowered to -33 ° C. A total of 28 ml of the Grignard reagent is added to the slurry over 2.0 hours. The temperature is maintained in the range -33 ° C to -38 ° C during this time. When the TLC shows the reaction to Δ ¹⁷ ( ²⁰ ) -corticoid silyl ether (II) is complete, the mixture is treated at −10 ° C. with 200 ml of 0.5 M ammonium chloride. The layers are separated and the organic layer is washed with 200 ml water. The separated aqueous layer is extracted with methylene chloride (2 x 50 ml). The organic extracts are combined and concentrated to give the corresponding Δ ¹⁷ ( ²² ) -corticoid silyl ether.

The material is dissolved in 100 ml of toluene. Sodium acetate 1.0
g, then 11.8 ml of 34% peroxyacetic acid is added at 16 ° C. The mixture is stirred at −16 to 10 ° C. for 19 hours, after which excess peracid is quenched with 1M sodium bisulfite. 100 ml of water are added and the layers are separated. The aqueous layer is extracted with 75 ml of toluene. The organic layers are washed successively with water (2 x 75 ml), then combined, filtered through a cotton cloth and concentrated. Dissolve the concentrate in methanol and re-concentrate to remove all toluene to give the corresponding 17α, 20-epoxide.

The 17α, 20-epoxide was treated with 40 m of methylene chloride under nitrogen.
Dissolve l and 70 ml of methanol. Adjust the temperature to 40 ° C and add 200mg potassium bicarbonate and potassium carbonate in 5ml water.
Add 200 mg of solution. The mixture is refluxed (about 42 ° C)
Stir at. After 75 minutes, TLC shows that both C ₂₀ trimethylsilyl and C ₂₁ acetate groups have been removed.
The reaction is stopped by adding 0.6 ml of acetic acid and the mixture is concentrated at atmospheric pressure to about 50 ml. About 0 of the obtained slurry
Cool to ° C, collect the solids, wash with cold methanol and dry under reduced pressure at 60 ° C to give the title compound. Melting point 260 ℃, decomposition.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01J 31/04 C07B 61/00 300

Claims (10)

[Claims] 1. A formula: In the copper catalyst to 16 unsaturated corticoids represented and group S _i
A formula characterized by contacting with a methylating agent in the presence of a silylating agent capable of introducing (R ₂₀ ) _3. [Wherein R ₂₀ is alkyl or phenyl having 1 to 4 carbon atoms, R ₂₀ may be the same or different; R ₂₁ is a hydrogen atom, —CO—R ₂₁ ′ or —S _i (R ₁₂₁ ) ₃ ; R ₂₁ 'and R ₁₂₁ are each alkyl or phenyl having 1 to 4 carbon atoms; delta ¹⁷ R ₁₂₁ is represented by the same or different can ⁽²⁰⁾ - a manufacturing method of a steroid. 2. A 16-unsaturated corticoid (I) is, delta ⁴ -
3-ketosteroid Δ ^1,4-3 -ketosteroid And 3β-hydroxy-Δ ⁵ -steroids And C ₃ protected forms of 3β-hydroxy-Δ ^5- (C) -steroids [In the formula, R ₃ is an alkyl group having 1 to ₃ carbon atoms, TMS, THP, or EEE group. R ₃ 'is alkyl or phenyl having 1 to 5 carbon atoms. R ₆ is hydrogen, a fluorine atom or a methyl group. R ₉ Hanashika, hydrogen, fluorine or oxygen atom, it is, C-ring a) a case of R ₉ Ganashi, delta ^{9 (11),} and b) R ₉ and R ₁₁ together oxygen atom If it is,
Use 9β, 11β-epoxide. R ₁₁ is a hydrogen or oxygen atom, two hydrogen atoms, or α
-Or a β-hydroxyl group or a trimethylsilyl ether thereof, which forms a C-ring, a) when R ₁₁ is a hydrogen atom, Δ ⁹ ( ¹¹ ), b) when R ₉ and R ₁₁ together are an oxygen atom. Yes, between C ₁₁ and R ₁₁ Is a single bond, 9β, 11β-epoxide, and c) R ₁₁ is an oxygen atom, and between C ₁₁ and R ₁₁ . If is a double bond, it is a ketone. R ₂₀ is alkyl having 1 to 4 carbon atoms or phenyl, and R 20
_Twenty can be the same or different. R ₂₁ is a hydrogen atom, —CO—R ₂₁ ′ or —S _i (R ₁₂₁ ) ₃ . R ₂₁ ′ is alkyl having 1 to 4 carbon atoms or phenyl. R ₁₂₁ is alkyl or phenyl having 1 to 4 carbon atoms,
R ₁₂₁ can be the same or different. ~ Indicates that the linking group can be either in the α or β sequence. Is a single or double bond; TMS is trimethylsilyl; THP is tetrahydropyranyl; EEE is (1-ethoxy) ethyl ether, [-O-CH (C
H ₃ ) OCH ₂ CH ₃ ]]. 3. A methylating agent is represented by the formula: CH ₃ Cu, (CH ₃ ) ₂ CuM or CH ₃ MgQ [wherein M represents a lithium or magnesium ion and Q represents a chlorine, bromine or iodine atom]. The method of paragraph 1 selected from the group consisting of: 4. The method according to claim 3, wherein the methylating agent is CH ₃ MgQ. 5. A cupric salt selected from the group consisting of cupric acetate, cupric chloride, cupric sulfate, or cuprous chloride, cuprous chloride, cuprous bromide, cuprous iodide. The method of the above item 1 which is a cuprous salt selected from the group consisting of copper and cuprous cyanide and a complex thereof. 6. The method of claim 1 wherein the copper catalyst is cupric acetate. 7. A silylating agent is (R ₂₀ ) _3- Si-E, bistrimethylsilylacetamide [E is a chlorine, bromine or iodine atom or -NR _α R _β , R _α and R _β are the same or different, and Alkyl or phenyl having 1 to 5 atoms, and R _α and R _β may be linked or cyclized with or without oxygen or even nitrogen atoms. R ₂₀ is the same as the above 1st item]. 8. The method of claim 1 wherein the silylating agent is trimethylsilyl chloride. 9. A 16-unsaturated corticoid (I) is 21-hydroxypregna-1,4,9 (11), 16-tetraene-3,20-.
Dione 21-acetic acid ester or 9β, 11β-epoxy-2
The method of paragraph 1 selected from the group consisting of 1-hydroxypregna-1,4,16-triene-3,20-dione 21-acetic acid ester. 10. The method of claim 1 wherein the silylating agent is present when the enolate intermediate is formed.